There have been torque fluctuation absorbing devices widely known, which are able to absorb torque fluctuation generated between a driving power source (e.g., an internal combustion engine and an electric motor) and a transmission. A conventional torque fluctuation absorbing device is provided with a damping mechanism, which is capable of absorbing fluctuation of a torque transmitted to a flywheel from the driving power source, and a limiter portion, which is capable of limiting a torque to be transmitted from the flywheel to a transmission input shaft when a fluctuating torque between the damping mechanism and the flywheel reaches a predetermined value, i.e., a limit torque value. The flywheel is connected to the driving power source, such as a crankshaft of the internal combustion engine.
The damping mechanism is connected to the transmission input shaft. The damping mechanism includes frictional members that are respectively attached at both surfaces at an outer circumferential portion of a damper disc. At the limiter portion, the frictional members of the damping mechanism is frictionally engaged with the flywheel in a direct manner or in an indirect manner via a frictional plate. The limit torque value, at which the frictional members at the limiter portion starts slipping, varies across the ages in response to the number of the operations of the limiter portion. Therefore, when the limit torque value widely increases, an excessive torque may be inputted to the transmission. On the other hand, when the limit torque value widely decreases, the frictional members may be transmitted with a torque smaller than a normal torque. In this case, a sufficient torque may not be transmitted to the transmission such that a vehicle accelerating performance may be deteriorated. Frictional powder of the frictional members seems to be one of the factors causing the above.
In light of foregoing, JP2003-194095A2 discloses a torque fluctuation absorbing device having frictional members at a limiter portion, both of which have penetrating slits in order to emit the frictional powder of the frictional members into an external ambient environment by a centrifugal force. Accordingly, the limit torque value can be effectively stabilized.
However, in the above-described torque fluctuation absorbing device, a frictional surface of each frictional member at the limiter portion can more stably and frictionally engaged with the flywheel so as to stabilize the limit torque value more reliably.
A need exists for providing an improved torque fluctuation absorbing device capable of reducing a fluctuation of a limit torque value, especially an age-based change of a limit torque value.